Converting an SVG to absolute command in Ruby - ruby

Question

I see that converting SVGs to absolute commands is a common ask:
Is there a tool to convert SVG line paths from absolute to relative?
Convert SVG Path to Absolute Commands
However, it looks like most solutions are in JavaScript:
Utility: Convert SVG path to all-relative or all-absolute commands
fontello/svgpath
Was wondering if anyone knew of a working solution in Ruby? Or a related tool that might make creating a solution easier? I believe it'd have to "work out what that last coordinate is in absolute terms"
I've found some Ruby projects related to SVGs but they don't seem like they'd be helpful in creating a solution:
DannyBen/victor
awebneck/savage
aseldawy/rasem
Hoping this already exists somewhere. I guess an alternative to creating it in Ruby is to figure out a way to execute JavaScript code in my project (API running Sinatra). I'd need to output the SVG as a string to Ruby though. I'm not sure about how to go about that or if it's feasible

Answer 1

Indeed, you need to work it out by yourself. Notice that an SVG file is not an SVG path, the former is a full-fledged XML document, while the latter is a specific attribute of some of the elements of a SVG.
So you get your path (say M 10,10 L 20,10 40,15), tokenize it using a finite state machine, and push fully formed tokens (adding the implicit letter repetitions) down an enumerable stream, obtaining
["M", 10, 10]
["L", 20, 10]
["L", 40, 15]
Then you can pass this stream to something like each_with_object so the object keeps track of the current position:
tokens.each_with_object([0, 0]).map do |command, current|
case command
in ["M", new_x, new_y]
# compute new command with relative syntax
modified = ["m", new_x - current.first, new_y - current.last]
# update current position
current.first = new_x
current.last = new_y
# yield the modified command
modified
in ["m", new_x, new_y]
# update current position
current.first += new_x
current.last += new_y
# yield the original command
["m", new_x, new_y]
end
end
You have to add all of the SVG path commands (https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/d), and change the corresponding absolute ones into relative. It will take 10' maximum to complete and you'll have a working SVG tool.